Difluprednate (6.alpha.,9.alpha.-difluoroprednisolone 17-butyrate 21-acetate) is an antiinflammtory steroid developed for local application, and is known to show superior antiinflammatory action by percutaneous administration (U.S. Pat. Nos. 3780177, 3784692). Difluprednate reportedly shows superior anti-inflammatory action and antiallergic action by percutaneous administration and subcutaneous administration [Pharmacometrics, 29 (3), 343-353 (1985), Pharmacometrics, 29 (3), 355-362 (1985)]. In view of such pharmacological actions, difluprednate is currently used mainly as a therapeutic drug for skin disorders such as eczema and dermatitis in the form of an ointment or a cream.
It is also expected that difluprednate will be effective for the treatment of various eye disorders by local administration to the eye, since difluprednate has superior antiinflammatory action and antiallergic action. The aforementioned U.S. Pat. Nos. 3780177, 3784692 detail formulation of difluprednate into an eye ointment for local administration to the eye. However, when a local administration to the eye is desired, an eye ointment is not entirely easy to use. Accordingly, formulation into an eye drop is preferred for the reason of easy administration. However, difluprednate has low solubility in water and preparation of a stable eye drop containing difluprednate at a therapeutically effective concentration is difficult. Thus, a pharmaceutical preparation of difluprednate which can be instilled to the eye has not been provided.